This invention relates to an apparatus and a process for producing ink reservoir elements for use in marking or writing instruments, and to the ink reservoir element itself.
Ink reservoir elements for use in marking and writing instruments have conventionally been formed of a fibrous bundle compacted together into a rod-shaped unit having longitudinal capillary passageways which extend therethrough between the fibers and which serve to hold the ink and release it at the required controlled rate. For a number of years, the fibrous material generally employed was cellulose acetate fibers, which could readily be heatbonded together with suitable plasticizers into a unitary body, and which were compatible with all of the ink formulations then in use. In recent years, however, ink formulations became more sophisticated so that the writing instruments did not need to be capped to prevent the ink from evaporating. Such new ink formulations required formic acid, which was not compatible with cellulose acetate. For this reason, various thermoplastic fibers and, in particular, polyester fibers, had to be used in place of the cellulose acetate fibers for producing the ink reservoir elements.
Efforts to make polyester fibers into a unitary ink reservoir body have included use of adhesives to bond polyester fibers together, and have also included use of film-overwrapped polyester fiber ink reservoir elements.
Efforts made to heat-bond the polyester fibers to each other without any additive adhesive have not met with much success. Because of the narrow softening point of polyester, it has not been possible to heat-bond drawn polyester fibers such as tow. Undrawn polyester fibers could be heat-bonded together, but produced an unusable product because of shrinkage during processing and lack of stability in the presence of inks at the temperature required for storage of writing instruments. Consequently, polyester fiber ink reservoir elements have heretofore been commercially produced in the form of an unbonded bundle of fibers compacted and held together in a rod-shaped unit by means of a porous film overwrap, and generally including a small diameter plastic "breather" tube disposed between the fibrous bundle and the overwrap and serving as an air release passage. Sometimes, the design of the writing instrument barrel precludes the necessity of a separate "breather" tube.
The film-overwrapped polyester fiber ink reservoir elements, when made with parallel continuous-filament fibers, have had adequate ink holding capacity and ink release properties for use with certain types of marking or writing instruments, for element, those employing fiber tips. However, they have not been successful with the more recent roller marker type of writing instrument, due to the fact that the roller markers require a faster ink release than the conventional fiber tips. Efforts to lower the fiber density and/or change the fiber size to increase the ink release have had limited success because the release is not uniform from start to finish. Also, lowering the fiber density has been found to reduce the ink holding capacity of the reservoir. Forming the reservoir from staple fibers randomly laid, rather than from continuous-filament parallel fibers, has been found to increase the ink release properties of short-length reservoirs, but at the longer lengths required for adequate ink holding capacity, this construction lacks the capillarity to function. Thus, it has not previously been possible to form a polyester fiber ink reservoir element having the proper combination of ink holding capacity and ink release properties satisfactory for use in the roller marker type of writing instrument.
U.S. Pat. No. 4,286,005 issued to Berger relates to an ink reservoir element useful with various types of marking or writing instruments, including roller markers. The ink reservoir element has a combination of ink holding capacity and ink release properties for use with such roller markers. The element is formed of a coherent sheet of flexible thermoplastic fibrous material composed of an interconnecting network of randomly arranged, highly dispersed, continuous-filament junctions. The embossed sheet is formed or compacted and bonded into a dimensionally stable rod-shaped body whose longitudinal axis extends parallel to the embossed grooves. The ink reservoir element is provided with at least one longitudinal peripheral slot extending continuously the entire length of its body and serving as an air release passage if a "breather" passage is required for the particular barrel design. Such ink reservoir construction is compatible with all inks presently being employed and exhibits the proper combination of ink holding capacity and ink release properties so as to render it suitable for use with various types of writing instruments, including roller markers and plastic nibs. This reservoir element requires the use of relatively expensive material, having a complex shape, and has not found commercial acceptance for this reason. This product is not known to prevent pen "leakers".
U.S. Pat. No. 3,094,736 to Bunzl et al teaches a marking device having as the adsorbent body thereof a tow or tow segment comprising continuous filaments randomly oriented primarily in a longitudinal dimension and bonded at a plurality of spaced locations by a plasticizer for such filaments. An impermeable overwrap for such body is used to give rigidity to the body and serve as a handling casing. Filamentary tow was with its filament randomly oriented primarily in a longitudinal direction, and bonded at a plurality of spaced locations by a plasticizer for the filaments. The term "filamentary tow" is defined in this patent, and such continuous filamentary tows are also known in U.S. Pat. Nos. 3,095,343 and 3,111,702. These tows usually comprise at least 50% cellulose acetate fibers. Such tow bodies, bound with plasticizers, provide rigidity.
U.S. Pat. No. 3,111,702 relates to products formed from continuous filamentary tows and also shows in FIG. 2 of the patent an apparatus for handling and steam-treating a tow; this patent is expressly incorporated by reference herein. This reference discusses forming a continuous body of fibers randomly oriented primarily in a longitudinal direction. The phrase, "randomly oriented primarily in a longitudinal direction" is intended to describe the condition of a body of fibers which are, as a whole, longitudinally aligned and which are, in the aggregate, in a parallel orientation, but which have short portions running more or less at random in non-parallel diverging and converging directions. This patent teaches bonding, tensioning and impregnating a raw tow into a plasticizer-impregnated layer of continuous uncrimped filaments, and then curing the continuous filamentary tow simultaneously with, or immediately after, gathering of such impregnated layer into a final raw shape. Apparatus is shown for handling such raw tow. The raw tow is taken from a supply bale through a device having jets to separate the tow, and a plasticizing device adds plasticizer to the fibers. The fibers are simultaneously gathered together and heated, thereby comprising a curing station.
Ink reservoir elements made by the prior art inventions are not compatible with some of the newer ink formulas, which have been changed from the prior art ink formulas in a manner which makes them incompatible with acetate. The use of film-wrapped ink reservoir elements binding polyester tow, having fibers which are substantially entirely parallel to one another, was made to attempt to overcome the deficiency of prior acetate fiber ink reservoir elements, so as to make the film-wrapped elements useable with such inks. With the introduction of the roller marker, a wetter system was required than is required with the conventional nib system. Two problems occured with such reservoir elements made from tow; (1) in order to achieve the wet system required for the roller markers, the low density polyester tow reservoir elements formed a very soft "rod" which gave difficulty in automatic handling equipment; and (2) these units held the ink so loosely that when they were dropped, "leakers" in these pens occured. Such "leakers" are tested for by dropping pens point first onto a hard surface. Should ink leak or spurt out, the pen is judged to be a "leaker". Such "leakers" are highly undesirable.
To attempt to overcome such pen leakers, polyester sliver having random fibers was used to attempt to hold the ink better at lower densities. These sliver-type polyester elements still had problems: (1) they still did not overcome the softness problem; and (2) such sliver is not uniform and therefore weights can vary excessively making it difficult to control ink flow to the roller marker.
The present invention relates to ink reservoirs using as a raw material stretch yarn, often referred to as "false twist stretch yarn". A number of patents are known relating to such "false twist" stretch material. Such material has unusual properties including the abiltity to stretch and curl or twist.
Such patents include for example, U.S. Pat. No. 3,747,318 relating to false-twist texturing yarn with a torque jet; U.S. Pat. No. 3,774,388 to a method for producing synthetic torque yarns; U.S. Pat. No. 4,395,871 to a process for the manufacture of twistless or substantially twistless yarn; U.S. Pat. No. 3,987,614 to a voluminous filament yarn having three-dimensionally curled filaments without loops; U.S. Pat. No. 3,638,410 teaching textured filaments and using "den" terminology and other terminology peculiar to this art; and U.S. Pat. No. 3,938,314 showing a false-twist texturing process using hollow friction twist tubes and discussing "denier" count of the yarn to be crimped as well as other terminology used in this art.